That's just oxidation. Not heat. If that was heat, it would have melted the insulation on leads to pins 1-3. Same kinda coloration happens to collectable coins. Your maybe thinking about annealing (used to strengthen rifle brass). You could try some contact cleaner and some Cpap smear swabs ( little brush on a stick) and scrub it. Try a wood qtip for extra strength if needed. Stay away from steel wool, and sand paper, try to solve the issue chemically.